Caption: Perpendicular polarizing filters. Composite image of two polarizing ultraviolet (UV) filters overlapped perpendicular to each other and annotated with arrows (blue) to show the orientation of the filters. The transmission of light through the overlapped filters in this case is close to zero. Polarizing filters absorb or reflect light that is polarized perpendicular to their polarizing axis. When they are parallel to each other, the transmission is maximised. When they are perpendicular to each other (an angle of 90 degrees), the transmission falls to close to zero (black area). When at a relative angle of 45 degrees, the transmission is between these values.